Luminaires are often subject to the requirement that they can emit their light directly and indirectly. A luminaire emits its light directly if the light is emitted directly onto the surface to be illuminated and indirectly if the light is emitted in the direction of a reflective surface, that is to say usually a wall or ceiling, and is directed from there to the region that is actually to be illuminated. In this case, it is known from the prior art to provide separate light modules having light emitting diodes for the direct portion and for the indirect portion of the light. These modules are generally supplied by different operating devices or one portion of the parallel-connected circuit branches is provided for the indirect lighting, and the other portion of the circuit branches for the direct lighting. It is obvious that operating the light modules with different operating devices is costly in terms of wiring and with regard to the space requirement. Less obvious is the problem that arises if parallel-connected circuit branches are used for dividing the direct and indirect portions.
In order that a clearly defined current flows in the circuit branches, said current being a prerequisite for a uniform loading of the light emitting diodes, it is absolutely necessary to use exclusively light emitting diodes of the same voltage bin. Binning is understood to mean the sorting of light emitting diodes in accordance with graded parameters such as color temperature, brightness, forward voltage (voltage binning), etc. This is necessary in order to handle production-dictated deviations in the parameters of the light emitting diodes in such a way that they are not manifested disadvantageously during the operation of the light emitting diodes. Understandably binning leads to an additional logistical outlay.
If printed circuit boards for luminaires are equipped with light emitting diodes on both sides, i.e. on their front side and their rear side, a further problem arises. In the production process, in general, the front side is equipped with light emitting diodes in a first work step, and the rear side in a second work step. If the circuit branches having the light emitting diodes of the front side are in parallel with the light emitting diodes of the rear side, then, as explained above, this necessitates the use of light emitting diodes of the same voltage bin on the front and rear sides. In the production process, it must therefore be ensured that not all the light emitting diodes of a voltage bin are used up in equipping the first side.
The invention is based on the object of embodying a printed circuit board for luminaires in such a way that the abovementioned disadvantages particularly of binning are minimized. Moreover, the object is to enable a greater flexibility in the selection of the light emitting diodes.